Optically aligning a loadport on a process machine by transmitting light through a system of apertures

ABSTRACT

An apparatus and a method for aligning a loadport on a process machine are disclosed. The apparatus is constructed by a base plate, an alignment block mounted on the base plate, a light source and an optical detector. The alignment block is provided with an aperture extending longitudinally through the block, or formed in a T-shape extending both longitudinally and transversely through the block. The light source may be suitably a laser emission source, or a laser source that operates in a pulse mode. The diameter of the aperture provided in the alignment block should be sufficiently small, i.e. smaller than 5 mm, and preferably smaller than 3 mm.

FIELD OF THE INVENTION

The present invention generally relates to an apparatus and a method foraligning a loadport on a process machine and more particularly, relatesto an apparatus for aligning a loadport on a process machine whichconsists of a base plate and an alignment block with an aperturetherethrough for passage of an alignment laser beam and a method forusing the apparatus.

BACKGROUND OF THE INVENTION

In the fabrication of a product, the product is usually processed atmany work stations or processing machines. The transporting or conveyingof partially finished products, or work-in-process (WIP) parts, is animportant aspect in the total manufacturing process. The conveying ofsemiconductor wafers is especially important in the manufacturing ofintegrated circuit chips due to the delicate nature of the chips.Furthermore, in fabricating an IC product, a multiplicity of fabricationsteps, i.e., as many as several hundred, is usually required to completethe fabrication process. A semiconductor wafer or IC chips must betransported between various process stations in order to perform variousfabrication processes.

For instance, to complete the fabrication of an IC chip, various stepsof deposition, cleaning, implantation, etching and passivation must becarried out before the chip can be packaged for shipment. Each of thesefabrication steps must be performed in a different process machine, i.e.a chemical vapor deposition chamber, an ion implantation chamber, anetcher, etc. A partially processed semiconductor wafer must be conveyedbetween various work stations many times before the fabrication processis completed. The safe conveying and accurate tracking of suchsemiconductor wafers or work-in-process parts in a semiconductorfabrication facility is therefore an important aspect of the totalfabrication process.

Conventionally, partially finished semiconductor wafers or WIP parts areconveyed in a fabrication plant by automatically guided vehicles oroverhead transport vehicles that travel on predetermined routes ortracks. For the conveying of semiconductor wafers, the wafers arenormally loaded into cassettes pods, such as SMIF (standard machineinterface) or FOUP (front opening unified pod), and then picked up andplaced in the automatic conveying vehicles. For identifying and locatingthe various semiconductor wafers or WIP parts being transported, thecassettes or pods are normally labeled with a tag positioned on the sideof the cassette or pod. The tags can be read automatically by a tagreader that is mounted on the guard rail of the conveying vehicle.

In an automatic material handling system (AMHS), stockers are used inconjunction with automatically guided or overhead transport vehicles,either on the ground or suspended on tracks, for the storing andtransporting of semiconductor wafers in SMIF pods or in wafer cassettes.For instance, three possible configurations for utilizing a stocker maybe provided. In the first case, a stocker is utilized for storing WIPwafers in SMIF pods and transporting them first to tool A, then to toolB, and finally to tool C for three separate processing steps to beconducted on the wafers. After the processing in tool C is completed,the SMIF pod is returned to the stocker for possible conveying toanother stocker. The configuration in the first case is theoreticallyworkable but hardly ever possible in a fabrication environment since thetools or processing equipment cannot always be arranged nearby toaccommodate the processing of wafers in the stocker.

In the second case, a stocker and a plurality of buffer stations A, Band C are used to accommodate different processes to be conducted intool A, tool B and tool C. A SMIF pod may be first delivered to bufferstation A from the stocker and waits there for processing in tool A.Buffer stations B and C are similarly utilized in connection with toolsB and C. The buffer stations A, B and C therefore become holdingstations for conducting processes on the wafers. This configurationprovides a workable solution to the fabrication process, however,requires excessive floor space because of the additional buffer stationsrequired. The configuration is therefore not feasible for use in asemiconductor fabrication facility.

In the third case, a stocker is provided for controlling the storage andconveying of WIP wafers to tools A, B and C. After a SMIF pod isdelivered to one of the three tools, the SMIF pod is always returned tothe stocker before it is sent to the next processing tool. This is aviable process since only one stocker is required for handling threedifferent processing tools, and in that no buffer station is needed.This configuration illustrates that the frequency of use of the stockeris extremely high since the stocker itself is used as a buffer stationfor all three tools. The accessing of the stocker is therefore morefrequent than that required in the previous two configurations.

FIG. 1 illustrates a schematic of a typical automatic material handlingsystem 20 that utilizes a central corridor 22, a plurality of bays 24and a multiplicity of process machines 26. A multiplicity of stockers 30are utilized for providing input/output to bay 24, or to processingmachines 26 located on the bay 24. The central corridor 22 designed forbay lay-out is frequently used in an efficient automatic materialhandling system to perform lot transportation between bays. In thisconfiguration, the stockers 30 of the automatic material handling systembecome the pathway for both input and output of the bay. Unfortunately,the stocker 30 frequently becomes a bottleneck for internaltransportation. It has been observed that a major cause for the stockers30 to be the bottleneck is the input/output ports of the stockers.

In modern semiconductor fabrication facilities, especially for the 200mm or 300 mm FAB plants, automatic guided vehicles (AGV) and overheadhoist transport (OHT) are extensively used to automate the wafertransport process as much as possible. The AGV and OHT utilize theinput/output ports of a stocker to load or unload wafer lots, i.e.normally stored in POUFs. FIG. 2 is a perspective view of an overheadhoist transport system 32 consisting of two vehicles 34,36 that travelon a track 38. An input port 40 and an output port 42 are provided onthe stocker 30. As shown in FIG. 2, the overhead transport vehicle 36stops at a position for unloading a FOUP 44 into the input port 40. Thesecond overhead transport vehicle 34 waits on track 38 for input fromstocker 30 until the first overhead transport vehicle 36 moves out ofthe way.

Similarly, the OHT system is used to deliver a cassette pod such as aFOUP to a process machine. This is shown in FIG. 3. A cassette pod 10 ofthe FOUP type is positioned on a loadport 12 of a process machine 14.The loadport 12 is frequently equipped with a plurality of locating pins16 for the proper positioning of the cassette pod 10. A detailedperspective view of the FOUP 10 is shown in FIG. 4. The FOUP 10 isconstructed by a body portion 18 and a cover portion 28. The bodyportion 18 is provided with a cavity 46 equipped with a multiplicity ofpartitions 48 for the positioning of 25 wafers of the 300 mm size. Thebody portion 18 is further provided with sloped handles 50 on both sidesof the body for ease of transporting. On top of the body portion 18, isprovided with a plate member 52 for gripping by a transport arm (notshown) of the OHT system (not shown).

When an OHT system is utilized to transport a cassette pod to a processmachine, problems arise when the loadport of the process machine is notin alignment with the OHT system. Mis-positioned cassette pods on aloadport not only affects the operation of loading/unloading from thepod, but also in severe instances may cause the cassette pod to tip overand cause breakage of the wafers. Conventionally, a laser surveyinginstrument is used to align the cassette pod, i.e. or the loadport ofthe process machine, to an OHT system. While the laser equipment may beproperly used in a pilot plant setup, it cannot be practically used in afabrication facility for several reasons. First, the laser equipment iscostly and difficult to operate. Secondly, the laser emission is harmfulto human eyes and thus when used, disturbs other operators that areworking in the same intra-bay. In a production facility, there arefrequently 20 or 30 process machines lined up in an intra-bay area. Itis therefore difficult or impossible to use laser for aligning onemachine, while not disturbing the operations of the other machines.

In a new fabrication facility for 300 mm wafers, the OHT system is themost popularly used cassette transport system. It is therefore veryimportant to be able to align all the cassette pods or the loadports ofthe process machine in a straight line in the same OHT intra-bay toassure the integrity of the fabrication process. To ensure minimumdisturbance to the fabrication process, s the laser alignment equipmentcannot be used in a fabrication facility for the alignment of a singleprocess machine.

When installing a process machine, the center of the loadport of themachine must be aligned not only with an overhead hoist transportsystem, but also with the other loadports on the neighboring processmachines in order to assure the accurate delivery of a cassette pod tothe loadport. Conventionally, the loadport center is aligned manually bymaking mechanical measurements and by subsequent manual calibration. Themanual alignment process is tedious, time consuming and inaccurate.

It is therefore an object of the present invention to provide anapparatus for aligning a loadport on a process machine that does nothave the drawbacks or shortcomings of the conventional apparatus.

It is another object of the present invention to provide an apparatusfor aligning a loadport on a process machine that is a simple mechanicaldevice.

It is a further object of the present invention to provide an apparatusfor aligning a loadport on a process machine that utilizes an alignmentblock provided with an aperture extending longitudinally through theblock.

It is still another object of the present invention to provide anapparatus for aligning a loadport on a process machine that utilizes analignment block with an aperture therethrough and an optical source.

It is yet another object of the present invention to provide anapparatus for aligning a loadport on a process machine which includes analignment block with an aperture therethrough, a light source and anoptical detector.

It is still another further object of the present invention to provide amethod for aligning a loadport on a process machine that can be carriedout by projecting a light beam through a small aperture in an alignmentblock mounted on the loadport.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus and a method foraligning a loadport on a process machine are provided.

In a preferred embodiment, an apparatus for aligning a loadport on aprocess machine can be provided which includes a base plate that has aplanar top and bottom surface parallel to each other, the base plate hasat least two vertical through holes adapted for mating to at least twolocating pins on a top surface of the process machine; an alignmentblock which has a planar bottom surface that intimately mates the topplanar surface of the base plate, the alignment block has an apertureextending longitudinally therethrough parallel with the bottom surfaceof the alignment block, the aperture has an entrance end, an exit endand an inside diameter not larger than 5 mm; a light source positionedjuxtaposed to the entrance end of the aperture; and an optical detectorsituated to the exit end of the aperture for detecting any lighttransmitted through the aperture.

In the apparatus for aligning a loadport on a process machine, theaperture may be formed in a T-shape extending longitudinally andtransversely through the alignment block with an image splitter mountedat an intersection of the T. The image splitter may be a mirror, whilethe alignment block may be integrally formed with the base plate. Thebase plate and the alignment block may be fabricated of a rigidmaterial, or may be fabricated of a rigid plastic or aluminum. The lightsource may be a laser source, or a laser source that operates in a pulsemode. The alignment block may have a length not more than 150 mm, whilethe aperture in the alignment block may have a diameter not larger than3 mm.

The present invention is further directed to a method for aligning aloadport on a process machine which can be carried out by the operatingsteps of: providing a base plate that has a planar top and bottomsurface parallel to each other; mounting the base plate to a processmachine by engaging at least two vertical through holes to at least twolocating pins on a top surface of the process machine; providing analignment block which has an aperture extending longitudinallytherethrough parallel with a bottom surface of the alignment block, theaperture having an entrance end, an exit end and an inside diameter notlarger than 5 mm; mounting the alignment block on the base plate byengaging a planar bottom surface of the block intimately to the topplanar surface of the base plate; projecting a light beam into theentrance end of the aperture; and detecting any light transmittedthrough the aperture at the exit end of the aperture.

The method for aligning a loadport on a process machine may furtherinclude the step of forming the aperture in a T-shape extendinglongitudinally and transversely through the alignment block with animage splitter mounted at an intersection of the T. The method mayfurther include the step of providing the image splitter in a mirror, orthe step of forming the alignment block integrally with the base plate,or the step of fabricating the base plate and the alignment block in arigid material, such as plastic or aluminum. The method may furtherinclude the step of providing the light source in a laser source form oras a laser source that operates in a pulse mode. The method may furtherinclude the step of forming the alignment block to a length not morethan 150 mm, or the step of forming the aperture in the alignment blockto a diameter not larger than 3 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

FIG. 1 is a schematic illustrating a conventional automatic materialhandling system utilizing a central corridor for intra-bay transport.

FIG. 2 is a schematic illustrating a conventional overhead hoisttransport system for accessing a stocker.

FIG. 3 is a graph illustrating a cassette pod positioned on a loadportof a process machine.

FIG. 4 is a perspective view of a front opening unified pod (FOUP).

FIG. 5 is a perspective view of the present invention apparatusincluding a base plate and an alignment block.

FIG. 5A is a side view of the present invention alignment block equippedwith a light source and an optical detector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses an apparatus and a method for alligninga loadport on a process machine.

The apparatus includes a base plate, an alignment block, a light sourceand an optical detector. The base plate may be fabricated of a planartop and bottom surface that are parallel to each other, the plate has atleast two vertical through holes, and preferably three vertical throughholes that are adapted for mating to at least two locating pins, andpreferably three locating pins on a top surface of the process machine.The alignment block may have a planar bottom surface which intimatelymates to the top planar surface of the base plate. The alignment blockmay have an aperture that extends longitudinally therethrough parallelwith the bottom surface of the alignment block. The aperture may have anentrance end, an exit end and an inside diameter not larger than 5 mm.The light source, may be a pulsed laser source that is positionedjuxtaposed to the entrance end of the aperture such that a light beam ofsmall diameter, i.e. smaller than 3 mm, may be projected into theaperture. The optical detector is situated to the exit end of theaperture capable of detecting any light that is transmitted through theaperture.

The present invention alignment block may further be formed with anaperture that is T-shaped which extends both longitudinally andtransversely through the alignment block with an image splitter, i.e. amirror, mounted at an intersection of the T.

In the apparatus, the alignment block may be integrally formed with thebase plate, or may be separately formed and then mechanically attachedtogether. The base plate and the alignment block should be fabricated ofa rigid material that has dimensional stability in the temperature rangethat the calibration process for the loadport is normally conducted. Thealignment block may have a length of approximately 150 mm, andpreferably not larger than 200 mm. The aperture provided in thealignment block may have a diameter not larger than 5 mm, and preferablynot larger than 3 mm.

The present invention is a novel method for aligning a loadport, or acenter of a loadport on a process machine which can be carried out bythe steps of providing a base plate, mounting the base plate to aprocess machine, providing an alignment block, mounting the alignmentblock to the base plate, projecting a light beam into an aperture in thealignment block and detecting any light transmitted through the apertureat an exit end of the aperture. When the present invention method iscarried out, the center of the loadport can be located when the laserbeam passes the aperture in the alignment block. However, if the laserbeam is blocked by the alignment block, the center of the loadport isdisplaced. The present invention therefore provides an easy method forlocating the center of a loadport. The laser beam utilized can be astandard calibration type laser beam which provides a straight beampath. The two apertures provided in the T-shaped arrangement in thealignment block enables the present invention apparatus to be used forcalibrating in all three directions, i.e. X-axis, Y-axis and Z-axis. Thehorizontal aperture provides the calibration in the X-axis and Y-axis,while the vertical aperture provides the calibration in the Z-axis. Forinstance, when the height of the loadport is 900 mm±5 mm, the verticaldiameter of an ellipse is about 10 mm, i.e. the Z-axis tolerance. When alaser beam passes through both the horizontal aperture and the verticalaperture, the center of the loadport is located.

Referring now to FIG. 5, a present invention apparatus 60 is shown. Theapparatus 60 is constructed by a base plate 62 and an alignment block64. The base plate 62 is provided with at least two locating holes 66,and preferably equipped with three locating holes as shown in FIG. 5 formating to three locating pins 16 (shown in FIG. 3). The base plate 62should be fabricated in a thermally stable and rigid material such as arigid plastic or aluminum. The dimension of the base plate may be 350 mmlength, 350 mm width and 30 mm thickness.

An alignment block 64 is shown in both FIGS. 5 and 5A. The alignmentblock 64 is provided with a horizontal aperture 68 and a verticalaperture 70, with an image splitter 72 provided at the intersection ofthe two apertures 68,70. The diameter of the apertures 68, 70 should beless than 5 mm, and preferably less than 3 mm.

As shown in FIG. 5A, at the entrance end 74 of the horizontal aperture68 is provided a light source 76 such as a laser source that operates ina pulse mode. At the exit end 78 of the horizontal aperture 68 isprovided with an optical detector 80 for detecting any light thattransmits through the horizontal aperture 68. When the image splitter 72is used, a second optical detector (not shown) should be provided at theexit end of the vertical aperture 70. It should be noted that while itis desirable to provide the aperture in both the horizontal and verticaldirections inside the alignment block 64, such is not always necessary.For instance, for certain calibration procedures, only the horizontalaperture 68 is required.

The alignment block 64 should be fabricated of a thermally stable, rigidmaterial such as a rigid plastic or aluminum. A suitable dimension forthe alignment block 64 may be 150 mm in length, 150 mm in width, and 150mm in thickness.

The present invention novel apparatus and method for aligning a loadporton a process machine have therefore been amply described in the abovedescription and in the appended drawings of FIGS. 5 and 5A.

While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

Furthermore, while the present invention has been described in terms ofa preferred embodiment, it is to be appreciated that those skilled inthe art will readily apply these teachings to other possible variationsof the inventions.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows.

What is claimed is:
 1. An apparatus for aligning a loadport on a processmachine comprising: a base plate having a planar top and bottom surfaceparallel to each other, said base plate having at least two verticalthrough holes adapted for mating to at least two locating pins on a topsurface of said process machine; an alignment block having a planarbottom surface which intimately mates said top planar surface of thebase plate, said alignment block having an aperture extendinglongitudinally therethrough parallel with said bottom surface of thealignment block, said aperture having an entrance end, an exit end andan inside diameter not larger than 5 mm; a light source positionedjuxtaposed to said entrance end of the aperture; and an optical detectorsituated to said exit end of the aperture for detecting any lighttransmitted through said aperture.
 2. An apparatus for aligning aloadport on a process machine according to claim 1, wherein saidaperture being formed in a T-shape extending longitudinally andtransversely through said alignment block with an image splitter mountedat an intersection of said T.
 3. An apparatus for aligning a loadport ona process machine according to claim 2, wherein said image splitter is amirror.
 4. An apparatus for aligning a loadport on a process machineaccording to claim 1, wherein said alignment block being integrallyformed with said base plate.
 5. An apparatus for aligning a loadport ona process machine according to claim 1, wherein said base plate and saidalignment block being fabricated of a rigid material.
 6. An apparatusfor aligning a loadport on a process machine according to claim 1,wherein said base plate and said alignment block being fabricated of arigid plastic or aluminum.
 7. An apparatus for aligning a loadport on aprocess machine according to claim 1, wherein said light source is alaser source.
 8. An apparatus for aligning a loadport on a processmachine according to claim 1, wherein said light source is a lasersource that operates in a pulse mode.
 9. An apparatus for aligning aloadport on a process machine according to claim 1, wherein saidalignment block has a length not more than 150 mm.
 10. An apparatus foraligning a loadport on a process machine according to claim 1, whereinsaid aperture in said alignment block having a diameter not larger than3 mm.
 11. A method for aligning a loadport on a process machinecomprising the steps of: providing a base plate having a planar top andbottom surface parallel to each other; mounting said base plate to aprocess machine by engaging at least two vertical through holes to atleast two locating pins on a top surface of said process machine;providing an alignment block having an aperture extending longitudinallytherethrough parallel with a bottom surface of the alignment block, saidaperture having an entrance end, an exit end and an inside diameter notlarger than 5 mm; mounting said alignment block on said base plate byengaging a planar bottom surface of the block intimately to said topplanar surface of the base plate; projecting a light beam into saidentrance end of the aperture; and detecting any light transmittedthrough said aperture at said exit end of the aperture.
 12. A method foraligning a loadport on a process machine according to claim 11 furthercomprising the step of forming said aperture in a T-shape extendinglongitudinally and transversely through said alignment block with animage splitter mounted at an intersection of said T.
 13. A method foraligning a loadport on a process machine according to claim 12 furthercomprising the step of providing said image splitter in a mirror.
 14. Amethod for aligning a loadport on a process machine according to claim11 further comprising the step of forming said alignment blockintegrally with said base plate.
 15. A method for aligning a loadport ona process machine according to claim 11 further comprising the step offabricating said base plate and said alignment block in a rigidmaterial.
 16. A method for aligning a loadport on a process machineaccording to claim 11 further comprising the step of fabricating saidbase plate and said alignment block in a rigid plastic or aluminum. 17.A method for aligning a loadport on a process machine according to claim11 further comprising the step of providing said light source in a lasersource.
 18. A method for aligning a loadport on a process machineaccording to claim 11 further comprising the step of providing saidlight source in a laser source that operates in a pulse mode.
 19. Amethod for aligning a loadport on a process machine according to claim11 further comprising the step of forming said alignment block to alength not more than 150 mm.
 20. A method for aligning a loadport on aprocess machine according to claim 11 further comprising the step offorming said aperture in said alignment block to a diameter not largerthan 3 mm.